Among various lasers (light amplification by stimulated emission of radiation) currently finding applcations in various fields, there are metal vapor lasers, in which electric pulse discharge is brought about in a tube containing vapor of a metal such as copper, manganese, lead, gold, calcium, barium, thallium, bismuth, etc., whereby metal atoms are excited with an intensive resonant trapping phenomenon for stimulated emission. The metal vapor laser has high output and energy conversion efficiency compared to other lasers, such as solid lasers, semiconductor lasers operable at normal temperature and gas lasers except for carbon oxide lasers and iodine lasers.
In such metal vapor laser, the discharge produced in the metal vapor in the tube produces resonant transition of atoms to an excited state, and some of the excited atoms undergo transition to a ground state or a metastable state by naturally emitting fluorescent light. When an inverse population state is eventually brought about so that the population of the excited atoms is higher than that of the metastable atoms, the fluorescent light acts with the excited atoms to cause stimulated emission of a new light beam. The new light beam thus generated is amplified as it is reflected by mirrors to be partly output as a laser beam from the output mirror.
With a copper vapor laser using copper as a lasant, strong oscillation lines with wavelengths of 510.6 and 578.2 nanometers exist in the visible wavelength region, and as high output power of several to several hundred Watts or more can be obtained with as high energy conversion efficiency as 1 to 1.2%. Thus, this laser finds applications as an exciter for dye lasers for uranium isotope separation and so forth. In addition, research on its application has been made in medical, industrial and various other fields.
In the metal vapor laser, however, while the excited metal atoms (i.e., atoms at the upper laser level) undergo transition by fluorescent light emission to energy levels of the ground state or metastable state, the populations of laser transitions are at a lower laser level, which is metastable level higher than the energy level of the ground state. While the lifetime of excitation at the upper laser level is several hundred nanoseconds, the transition from the lower laser level to the ground state is a forbidden transition, and the lifetime of excitation excitation at the lower laser level is far longer, i.e., several to several ten microseconds. This means that the state of inverse population is terminated at the commencement of the laser oscillation. In other words, the prior art metal vapor lasers are self-terminating lasers with the output pulse duration of at most several to several ten nanosconds.
If the lifetime of excitation at the lower laser level could be curtailed, the inverse population time will naturally be extended to extend the laser output pulse duration. If this is realized, not only the laser conversion efficiency can be increase, but also the possibility of continuous oscillating operation can be increased. The utility of the metal vapor lasers thus can be increased so that the lasers can find effective applications in various fields.